(1) Field of the Invention
This invention relates to a novel pyrazole derivatives, method for preparation thereof, a selective herbicidal composition containing as an active ingredient one or more of said derivatives, and method for damaging and controlling weeds using said derivatives.
(2) Description of the Prior Art
Hitherto, some pyrazole derivatives having herbicidal activity has been known. For example, Japanese Patent Publication No. 36648/79 (corresponding to U.S. Pat. Nos. 4,063,925 and 4,146,726) and Japanese Laid-open Patent Publication No. 41872/79 (corresponding to U.S. Pat. No. 4,230,481) disclose certain 4-benzoyl derivatives of pyrazole which are useful for herbicids.
Among these pyrazole derivatives, however, only the pyrazolate represented by the formula below is used practically and commercially as an active ingredient of a herbicide for use in a paddy field as far as the present inventors' knowledge is concerned. ##STR3##
All the pyrazole derivatives disclosed by the above-mentioned publication No. 41872/79 have a lower alkyl group, specifically CH.sub.3 group, at 3-position of the pyrazole ring.
Also the majority of the pyrazole derivatives disclosed by the above-mentioned publication No. 36648/79 have a lower alkyl at the 3-position of the pyrazole ring and --OH, --SH, a salt thereof or an organic acid ester thereof at 5-position of said ring; among the pyrazole derivatives disclosed by said publication, only the compound of the following formula is exemplified as a pyrazole derivative having hydrogen atom at 3-position (i.e. unsubstituted at 3-position) of the pyrazole ring: ##STR4##
The compound B, however, is inferior to the commercialized compound A in herbicidal activity as is apparent from the biological test data given in the above-mentioned publication No. 36648/79.
Despite the fact that a number of pyrazole derivatives have been synthesized and the herbicidal activity thereof has been tested, there has not been found a pyrazole derivative which is unsubstituted at 3-position of the pyrazole ring and which exhibits herbicidal activity except the above-mentioned compound B.
This is because synthesis of pyrazole derivatives unsubstituted at 3-position has been very difficult while a pyrazole derivative substituted by an alkyl at 3-position has been relatively readily prepared, and because the former compound has been believed to be less active in herbicidal action and thus less practical than the latter one.
The present inventors have done intensive researches on pyrazole derivatives having hydrogen atom at 3-position of the pyrazole ring and have unexpectedly found that some of these pyrazole derivatives exhibit herbicidal action against a wide range of weeds, particularly against perennial weeds such as perennial flat sedge (Cyperus serotinus), bulrush (Scirpus hotarui) and perennial spikerush (Eleocharis kuroguwai) which have been difficult to control and against which no useful herbicide has been developed. Moreover, the present inventors have found a process for readily preparing such pyrazole derivatives to complete the present invention. The compounds according to the present invention have no phytotoxicity upon a paddy-rice plant and, thus, can be used with safety.